Hydroxyalkylation/alkylation of 2-methylfuran and furfural over niobic acid catalysts for the synthesis of high carbon transport fuel precursors†
In producing high-grade transport fuel from lignocellulosic biomass, carbon–carbon (C–C) coupling reactions are one of the most available and efficient strategies for increasing the carbon chain length and thereby producing fuel precursors. In this work, niobic acid catalysts (NAC) were prepared by facile precipitation and sol–gel process and were investigated for the solvent-free hydroxyalkylation/alkylation (HAA) of 2-methylfuran (2-MF) with biomass-derived compounds. The effect of thermal treatment (100–500 °C) on the properties and performance of niobic acid as a solid acid catalyst for the HAA reaction was explored. According to the results of characterization, the high activity of the niobic acid catalysts can be rationalized by their superior textural properties, strong acidity, good water tolerance ability, and by the presence of surface Nb–OH groups, which served as Brønsted acid sites. Among the catalysts tested, the NAC thermally treated at 400 °C (NAC400) exhibited the best catalytic performance, and under the optimized conditions, a maximum of 90% yield of C15 fuel precursor was obtained. Recyclability studies also demonstrated that NAC could be used for up to five reaction runs, thus, making it a promising solid acid catalyst for the C–C coupling of biomass-derived platform molecules to produce high carbon fuel precursors. Furthermore, a plausible HAA reaction mechanism over NAC was suggested.